Examples include the subacromial bursa that protects the tendon of shoulder muscle as it passes under the acromion of the scapula, and the suprapatellar bursa that separates the tendon of the large anterior thigh muscle from the distal femur just above the knee.
A tendon sheath is similar in structure to a bursa, but smaller. It is a connective tissue sac that surrounds a muscle tendon at places where the tendon crosses a joint. It contains a lubricating fluid that allows for smooth motions of the tendon during muscle contraction and joint movements.
Bursitis can be either acute lasting only a few days or chronic. It can arise from muscle overuse, trauma, excessive or prolonged pressure on the skin, rheumatoid arthritis, gout, or infection of the joint. Repeated acute episodes of bursitis can result in a chronic condition. Treatments for the disorder include antibiotics if the bursitis is caused by an infection, or anti-inflammatory agents, such as nonsteroidal anti-inflammatory drugs NSAIDs or corticosteroids if the bursitis is due to trauma or overuse.
Chronic bursitis may require that fluid be drained, but additional surgery is usually not required. Synovial joints are subdivided based on the shapes of the articulating surfaces of the bones that form each joint. The six types of synovial joints are pivot, hinge, condyloid, saddle, plane, and ball-and socket-joints Figure 9. At a pivot joint , a rounded portion of a bone is enclosed within a ring formed partially by the articulation with another bone and partially by a ligament see Figure 9.
The bone rotates within this ring. Since the rotation is around a single axis, pivot joints are functionally classified as a uniaxial diarthrosis type of joint.
An example of a pivot joint is the atlantoaxial joint, found between the C1 atlas and C2 axis vertebrae. Here, the upward projecting dens of the axis articulates with the inner aspect of the atlas, where it is held in place by a ligament. Rotation at this joint allows you to turn your head from side to side.
A second pivot joint is found at the proximal radioulnar joint. Here, the head of the radius is largely encircled by a ligament that holds it in place as it articulates with the radial notch of the ulna.
Rotation of the radius allows for forearm movements. In a hinge joint , the convex end of one bone articulates with the concave end of the adjoining bone see Figure 9. This type of joint allows only for bending and straightening motions along a single axis, and thus hinge joints are functionally classified as uniaxial joints. A good example is the elbow joint, with the articulation between the trochlea of the humerus and the trochlear notch of the ulna.
Other hinge joints of the body include the knee, ankle, and interphalangeal joints between the phalanges of the fingers and toes. At a condyloid joint ellipsoid joint , the shallow depression at the end of one bone articulates with a rounded structure from an adjacent bone or bones see Figure 9.
The knuckle metacarpophalangeal joints of the hand between the distal end of a metacarpal bone and the proximal phalanx are condyloid joints. Another example is the radiocarpal joint of the wrist, between the shallow depression at the distal end of the radius bone and the rounded scaphoid, lunate, and triquetrum carpal bones. In this case, the articulation area has a more oval elliptical shape.
Functionally, condyloid joints are biaxial joints that allow for two planes of movement. One movement involves the bending and straightening of the fingers or the anterior-posterior movements of the hand. The second movement is a side-to-side movement, which allows you to spread your fingers apart and bring them together, or to move your hand in a medial or lateral direction. At a saddle joint , both of the articulating surfaces for the bones have a saddle shape, which is concave in one direction and convex in the other see Figure 9.
This allows the two bones to fit together like a rider sitting on a saddle. Saddle joints are functionally classified as biaxial joints. The primary example is the first carpometacarpal joint, between the trapezium a carpal bone and the first metacarpal bone at the base of the thumb.
This joint provides the thumb the ability to move away from the palm of the hand along two planes. Thus, the thumb can move within the same plane as the palm of the hand, or it can jut out anteriorly, perpendicular to the palm.
The sternoclavicular joint is also classified as a saddle joint. At a plane joint gliding joint , the articulating surfaces of the bones are flat or slightly curved and of approximately the same size, which allows the bones to slide against each other see Figure 9.
The motion at this type of joint is usually small and tightly constrained by surrounding ligaments. Based only on their shape, plane joints can allow multiple movements, including rotation and can be functionally classified as a multiaxial joint. However, not all of these movements are available to every plane joint due to limitations placed on it by ligaments or neighboring bones.
Depending upon the specific joint of the body, a plane joint may exhibit movement in a single plane or in multiple planes. Plane joints are found between the carpal bones intercarpal joints of the wrist or tarsal bones intertarsal joints of the foot, between the clavicle and acromion of the scapula acromioclavicular joint , and between the superior and inferior articular processes of adjacent vertebrae zygapophysial joints.
The joint with the greatest range of motion is the ball-and-socket joint. At these joints, the rounded head of one bone the ball fits into the concave articulation the socket of the adjacent bone see Figure 9.
The hip joint and the glenohumeral shoulder joint are the only ball-and-socket joints of the body. At the hip joint, the head of the femur articulates with the acetabulum of the hip bone, and at the shoulder joint, the head of the humerus articulates with the glenoid cavity of the scapula. Ball-and-socket joints are classified functionally as multiaxial joints. The femur and the humerus are able to move in both anterior-posterior and medial-lateral directions and they can also rotate around their long axis.
The shallow socket formed by the glenoid cavity allows the shoulder joint an extensive range of motion. Smooth cartilage prevents friction as the bones move against one another. In freely movable joints, the entire joint is enclosed inside a membrane filled with lubricating synovial fluid, which helps to provide extra cushioning against impact. Muscles are attached to bones with thick, tough bands of connective tissue called tendons. Where tendons lie close to bone, tiny sacs called bursae sit between the tendon and the bone to reduce friction.
A bursa is filled with synovial fluid. This page has been produced in consultation with and approved by:. The abdominal muscles support the trunk, allow movement and hold organs in place by regulating internal abdominal pressure.
Acromegaly is caused by an excess of growth hormone in adults, which causes the overgrowth of bones in the face, hands, feet and internal organs.
Exercise can prevent age-related changes to muscles, bones and joints and can reverse these changes too. A person with amyloidosis produces aggregates of insoluble protein that cannot be eliminated from the body. Ankle sprain is a common sports injuries caused by overstretching and tearing the supporting ligaments. Content on this website is provided for information purposes only.
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The information and materials contained on this website are not intended to constitute a comprehensive guide concerning all aspects of the therapy, product or treatment described on the website. All users are urged to always seek advice from a registered health care professional for diagnosis and answers to their medical questions and to ascertain whether the particular therapy, service, product or treatment described on the website is suitable in their circumstances.
The State of Victoria and the Department of Health shall not bear any liability for reliance by any user on the materials contained on this website. When you decide to move, the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract.
The motor cortex on the right side of the brain controls the muscles on the left side of the body and vice versa. The cerebellum coordinates the muscle movements ordered by the motor cortex.
Sensors in the muscles and joints send messages back through peripheral nerves to tell the cerebellum and other parts of the brain where and how the arm or leg is moving and what position it's in. This feedback results in smooth, coordinated motion. If you want to lift your arm, your brain sends a message to the muscles in your arm and you move it. When you run, the messages to the brain are more involved, because many muscles have to work in rhythm.
Muscles move body parts by contracting and then relaxing. Muscles can pull bones, but they can't push them back to the original position. So they work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint. Then, when the movement is completed, the flexor relaxes and the extensor contracts to extend or straighten the limb at the same joint.
For example, the biceps muscle, in the front of the upper arm, is a flexor, and the triceps, at the back of the upper arm, is an extensor. When you bend at your elbow, the biceps contracts. Then the biceps relaxes and the triceps contracts to straighten the elbow. Joints are where two bones meet. They make the skeleton flexible — without them, movement would be impossible. Joints allow our bodies to move in many ways. Some joints open and close like a hinge such as knees and elbows , whereas others allow for more complicated movement — a shoulder or hip joint, for example, allows for backward, forward, sideways, and rotating movement.
Reviewed by: KidsHealth Medical Experts. Larger text size Large text size Regular text size. It provides a cushion between bones and tendons or muscles around a joint. This helps to reduce friction between the bones and allows for free movement. Bursae occur at sites of shearing in subcutaneous tissue or between deeper tissues such as muscle groups and fascia. Many bursae develop during growth, but new or adventitious bursae can occur at sites of occupational friction.
Bursae are found around most major joints of the body, such as the shoulder and the knee. For example, to protect the knee and reduce friction from the various muscles, tendons, and ligaments that attach to and cross the knee joint, knees are cushioned by 14 different bursae: five in front, four laterally, and five medially.
A tendon is a mechanism by which muscles connect to bone and that transmits force. However, over the past two decades, research has also characterized the elastic properties of tendons and their ability to function as springs. This characteristic allows tendons to passively modulate forces during locomotion, thus providing additional stability with no active work.
It also allows tendons to store and recover energy with high efficiency. Achilles Tendon : The Achilles tendon, also called the calcaneus, provides stability and limits the range of motion at the ankle joint. During a human stride, the Achilles calcaneal tendon stretches as the ankle joint undergoes dorsiflexion. During the last portion of the stride, as the foot undergoes plantar flexion pointing the toes downward , the stored elastic energy is released.
Because the tendon stretches, the muscle is able to function with less or even no change in length, allowing it to generate greater force.
Certain joints exhibit special movements including elevation, depression, protraction, retraction, inversion, eversion, dorsiflexion, plantar flexion, supination, pronation, and opposition. A number of factors influence joint stability. These include:. Typically, the more stable the joint is, the less is its range of motion and vice versa. Aging is another factor that influences motion due to decreased fluid, thinning of cartilage, shortening of ligaments, and loss of flexibility.
A synovial joint, also known as a diarthrosis, is the most common and most movable type of joint in the body of a mammal. Synovial joints achieve movement at the point of contact of the articulating bones. Structural and functional differences distinguish synovial joints from cartilaginous joints synchondroses and symphyses and fibrous joints sutures, gomphoses, and syndesmoses.
Several movements may be performed by synovial joints. Abduction is the movement away from the midline of the body. Adduction is the movement toward the middle line of the body. Extension is the straightening of limbs increase in angle at a joint.
Flexion is bending the limbs reduction of angle at a joint. Rotation is a circular movement around a fixed point. Body Movements I : Image demonstrating the various joint movements. There are six types of synovial joints. Some are relatively immobile but more stable than mobile joints. Others have multiple degrees of freedom, but at the expense of greater risk of injury. The six types of joints include:. Six Types of Synovial Joints : Image demonstrating the six different types of synovial joints.
There are six different types of synovial joint based on their shapes, each allowing a different kind of movement. There are six basic types of synovial joints. Anatomical joints may consist of a combination of two or more joint types.
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